Apollo 13 lifted off on time from the Kennedy Space Center on Saturday, April 11, 1970 at 2:13pm EST. The first 55 hours and 55 minutes of the mission went smoothly until, just over 3/4 of the way to the Moon, shortly after the one and only TV transmission of their journey, Apollo 13 had a problem.
A liquid oxygen tank exploded, pushing the flight off course, robbing the capsule of breathable oxygen and fuel for power generation.
An accident investigation board later found that upgrades to the tank, designed by American Rockwell, had overlooked thermostatic switches while being made to work with higher voltage test equipment at the Kennedy Space Center. These switches were likely welded shut during preflight tests allowing temperatures in the tank to rise to over 12 times the original design's limits.
Systems, including guidance, were shut down to conserve power. Over the next 6 hours, the astronauts with assistance from flight controllers on the ground, manually calculated a free return trajectory to get them back home.
The crew used the on board sextant, which required no power, to determine their position looking for two stars from a list of 37 known to the guidance computer. This a common task used many times during all Apollo missions to provide updates to the guidance, but was particularly complex for Apollo 13.
Had everything gone to plan, NASA’s third mission to land astronauts on the moon would have deployed a pallet of science instruments and brought back samples from humanity’s first visit to the lunar uplands. Instead, 55 years ago this month, Apollo 13 “had a problem.”
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